current is higher than 1.0, the slope of the operation characteristic (ID/IB) is
constant at 50 percent. Different operating characteristics are possible based on
the
Operate value
setting.
For the protection of the trip, the measured neutral current has to be above 4
percent. When the condition has been fulfilled, the measured neutral current must
stay above 2 percent, otherwise reset time is started.
To calculate the directional differential current ID_COSPHI, the fundamental
frequency amplitude of both the residual and neutral currents has to be above 4
percent of In. If neither or only one condition is fulfilled at a time, the cosφ term
is forced to 1. After the conditions are fulfilled, both currents must stay above 2
percent of In to allow the continuous calculation of the cosφ term.
Second harmonic blocking
This module compares the ratio of the current second harmonic (I
0
_2H) and
fundamental component of I
0
to the set value
Start value 2.H
. If the ratio (I
0
_2H / I
0
) value exceeds the set value, the BLK2H output is activated.
The blocking also prevents unwanted operation at the recovery and sympathetic
magnetizing inrushes. At the recovery inrush, the magnetizing current of the
transformer to be protected increases momentarily when the voltage returns to
normal after the clearance of a fault outside the protected area. The sympathetic
inrush is caused by the energization of a transformer running in parallel with the
protected transformer connected to the network.
The second harmonic blocking is disabled when
Restraint mode
is set to "None" and
enabled when set to "Harmonic2".
Timer
Once activated, the Timer activates the START output. The time characteristic is
according to DT. When the operation timer has reached the value set by
Minimum
operate time
, the OPERATE output is activated. If the fault disappears before the
module operates, the reset timer is activated. If the reset timer reaches the value
set by
Reset delay time
, the reset timer resets and the START output is deactivated.
The Timer calculates the start duration value START_DUR which indicates the
percentage ratio of the start situation and the set operate time. The value is
available through the Monitored data view.
Blocking logic
There are three operation modes in the blocking function. The operation modes
are controlled by the BLOCK input and the global setting in Configuration>
System> Blocking mode which selects the blocking mode. The BLOCK input can
be controlled by a binary input, a horizontal communication input or an internal
signal of the protection relay's program. The influence of the BLOCK signal activation
is preselected with the global setting
Blocking mode
.
The
Blocking mode
setting has three blocking methods. In the "Freeze timers"
mode, the operate timer is frozen to the prevailing value, but the OPERATE output
is not deactivated when blocking is activated. In the "Block all" mode, the whole
function is blocked and the timers are reset. In the "Block OPERATE output" mode,
the function operates normally but the OPERATE output is not activated. The
activation of the output of the second harmonic blocking signal BLK2H deactivates
the OPERATE output.
Protection functions
1MRS759142 F
752 REX640
Technical Manual
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